Management of Ventilators Flashcards
Bellows Ventilator driving mechanism
- pneumatically (gas/air pressure) driven, electronically controlled (need electricity)
- movement is controlled by drive gas
Piston ventilator driving mechanism
- driven by electric motor (no electricity = no ventilation)
Excess gas and pressure is vented out to the scavenging system via the ____?
Spill valve
- Is pneumatically closed during inspiration so that positive pressure can be generated
- During exhalation, the pressurizing gas is vented out and the ventilator spill valve is no longer closed
In VCV, you set the ____ & _____. _____ will vary. ____ will remain constant.
Tv
RR
Peak Pressure
Mv
In VCV the PRESSURE tracing resembles what?
Shark Fins
In VCV the FLOW tracing resembles what?
Flow plateaus like a square, it delivers a constant flow during inhalation
In PCV, you set the ____ & _____. _____ & ____ will vary.
Peak Pressure
RR
Tv & Mv
In PCV the PRESSURE tracing resembles what?
Pressure plateaus like a square, it delivers a constant pressure during inhalation
In PCV the FLOW tracing resembles what?
Flow rises quickly to reach set pressure, and then decelerates
How does PCV-VG work?
It first delivers VCV breath to assess compliance. Then delivers a preset Tv with the lowest possible pressure for a set amount of mandatory breaths. Uses a decelerating flow pattern like pressure control does. The pressure adapts gradually over a few breaths if compliance changes.
How does PSV work?
- Used only for patients who are spont breathing
- We set the pressure support
- When vent senses an inspiratory effort from pt the vent provides pressure to the airway to reduce WOB
PSV-Pro
-back up ventilation
“apnea mode”
-back up mode is SIMV-PC
-we set minimum mandatory RR and pressure
-in between mandatory breaths the patient receives pressure support for their own breaths
SIMV
- combo of spont breathing and mandatory ventilation
- machine breaths are delivered at set intervals
- pt can take breaths in between with pressure support
Normal Tv
6 and 8 mL/kg IBW
400-700
Normal Mv
4000 - 8000
Normal I:E
1: 2
- longer E times if obstructive pulm disease
Normal PIP
~15-20
< 40
Normal PPlat
~10-15
< 30
Normal Pdrive
Pplat-PEEP
< 15
Normal PEEP
5-10
Normal PS
8-10
Normal Raw
2-5
PCV uses ____ flow while VCV uses ____ flow
- decelerating
- constant
How to determine I:E time for a RR of 20 & 10
RR of 20
60 / 20 = 3 seconds
1 second for insp and 2 seconds for exp
RR of 10
60 / 10 = 6
2 seconds for insp, 4 seconds for exp
Why would we change our I:E ratio?
Usually for patients with obstructive airway disease
1:3, 1:4
Severe ARDS sometimes inverse 1:2
How do you calculate total airway resistance?
Raw = PIP - Pplat
Define total airway resistance
- Measure of the impedance to ventilation flow caused by the movement of gas through the airway
- ratio of the change in driving PRESSURE to the change in FLOW rate
VC vs PC which is better for high resistance (like asthmatics)
- pressure control would be better
- rapid delivery of decelerating flow is more efficient at overcoming high resistance
- in PC the peak pressure is maintained throughout inhalation and usually improves oxygenation
How to overcome higher resistance for a given TV?
- using lower flow for longer time or higher driving pressure
What does Pplat represent?
- resting airway pressure during inspiratory pause
- the total respiratory system elastic recoil at end-inflation volume
- plateau pressure depends ONLY on COMPLIANCE and is not affected by resistance
Pplat tells us about ____ while PIP tells us about ____
Static compliance
Resistance
Airway Compliance
- ratio of a change in VOLUME to a change in PRESSURE
- total compliance = elasticity of the lungs, thorax, abd and breathing system
Static compliance
= Tv / Pplat - PEEP
- refers to the P/V relationship when air is NOT moving
Dynamic Compliance
Vt / PIP-PEEP
-refers to the P/V relationship when air IS moving
What decreases Static Compliance?
conditions that make it difficult to inflate the lungs (obesity, fibrosis, vascular engorgement, external compression-like surgeons elbow or tight dressings
What increases Static Compliance?
emphysema because it destroys the lung tissue and therefore reduces elastic recoil, resulting in lung air trapping
What decreases Dynamic Compliance
-airway obstructions such as foreign bodies and bronchospasm
Patients with obstructive lung pathology may require a longer (inspiration/expiration) time?
a longer expiratory time to avoid gas trapping
and thus increasing Co2 levels
How do muscle relaxants affect compliance?
- Using muscle relaxants will increase chest wall and abdominal compliance but NOT lung tissue compliance
- relaxed chest wall easier to inflate
Determining Compliance vs Resistance in VC Ventilation
- an increase in the difference between PIP and Pplat pressures = increase in resistance
- increase in Pplat = decrease in compliance
What happens if there is an increase in resistance?
- higher peak pressure will be necessary to produce the same flow
(plateau pressure depends ONLY on compliance and will not be affected by resistance)
High PIP with a high Pplat and a normal Raw (plateau to peak pressure difference) indicates what?
- that the problem is with our Pplat & our high peak pressures are due to compliance issues
Causes: COPD, Pulmonary Edema, Pneumo, atelectasis, pulmonary fibrosis, pressure on the thorax from the abdomen or external, lung hyperinflation or autopeeping
High PIP with a normal Pplat and an increased Raw (plateau to peak pressure difference) indicates what?
-That our high PIP pressures are due to increases in airway resistance
Causes: obstruction caused by mucus plug, kink in ETT, pt biting tube, R mainstem, bronchospasm, ETT size is too small
Most common problem/alarm with ventilation?
high peak pressures
How can we reduce high peak pressures?
-we want to increase compliance and decrease resistance in the system
- Decrease TV (may need to increase RR)
- Increase respiratory compliance (muscle relaxant, albuterol)
- increase inps time (I:E ratio, decrease RR, decrease insp flow time, change from VCV to PCV)
- reduce resistance (remember pouselles law, increase ETT size, decrease density of gas (heliox), decrease length of cricuit)
- reduce PEEP
High TV, Pplat can cause?
barotrauma
What may cause a Low pressure alarm?
Think air leak
- circuit disconnection
- ETT too high, ETT cuff leak
- gas/power supply loss
DOPES mnemonic
- Dislodgement
- Obstruction of the ETT from mucus plugs or from patients biting on the tube
- Pneumothorax
- Equipment malfunction
- Stacked Breaths or patient ventilator dyssynchrony
